Low noise charge gain hybrid imager
View Patent ↗In one aspect of the present application, provided is a charge gain imaging system and a method of operating the charge gain imaging system. The method includes collecting a pixel charge. The collected pixel charge being stored by a pixel capacitance (C p ). Thereafter the pixel having the stored pixel charge is selected via a pixel select switch, and the pixel voltage is transferred and stored by data line capacitance (C d ) of a data line of the imager. An amplifier select switch is activated connecting the data line to a charge amplifier, and a charge gain defined by a relationship C d /C p , is sensed by a charge amplifier.
1. A method of operating a charge gain hybrid imaging system comprising:
activating an amplifier reset switch to reset a charge amplifier;
collecting a charge of a pixel of the imaging system;
storing the collected pixel charge in a pixel capacitor (C p );
selecting the pixel via a pixel select switch;
activating a pixel reset switch to reset the pixel;
deactivating the amplifier reset switch, wherein a gate-source capacitive charge is injected into a front end of the charge amplifier;
transferring the pixel charge stored on the pixel capacitor (C p ) to a data line capacitor (C d ) of a data line until a full data line charge, which is associated with an effective charge gain of C d /C p , is reached;
activating an amplifier select switch connecting the data line to the charge amplifier, the gate-source capacitive charge detected by a first sampling action of a sample switch, wherein the active state of the amplifier select switch encompasses the first active state of the sample switch and the charge of the data line capacitance is transferred to the charge amplifier as the charge gain defined by the relationship C d /C p ;
sensing the data line charge by the charge amplifier;
deactivating the amplifier select switch after the pixel is selected, to isolate the pixel from the charge amplifier; and
activating the sample switch a second time, wherein an output of the charge amplifier due to the charge gain is detected.
2. The method according to claim 1 , wherein use of data line capacitance provides noise-immunity, linear charge detection.
3. The method according to claim 1 , wherein the step of selecting the pixel via the pixel select switch includes connecting a voltage amplifier of the pixel to a data line of the imaging system.
4. The method according to claim 3 , wherein the step of connecting the voltage amplifier of the pixel to the data line includes charging the data line to a charge value greater than the pixel charge.
5. The method according to claim 1 further including:
reading a signal from the charge amplifier based on the sensed charge gain, and
converting the readout signal to a digital signal.
6. The method according to claim 1 , wherein the pixel select switch is a transistor, and the step of selecting the pixel via the pixel select switch includes turning on the transistor by providing an input to the gate of the transistor.
7. The method according to claim 1 , wherein the pixel charge collection may be by a photoconductor, photodiode, gap cell, or other charge-generating transducer.
8. The method according to claim 1 , wherein the pixel is one of a plurality of pixels of a matrix of pixels, wherein each pixel of the matrix of pixels includes a transducer, a voltage amplifier and pixel capacitor.
9. The method according to claim 8 , wherein an amplifier select switch is provided with each pixel or row of the matrix of pixels.
10. The method according to claim 9 , wherein each row of the pixels of the matrix is selected by the amplifier select switch in sequence, wherein pixel charge from the selected pixels are transferred to the data line, and the charge gain for each pixel is then sensed by the charge amplifier, wherein each column comprised of rows is then selected.
11. A low noise hybrid imaging system comprising:
a pixel including,
a transducer configured to generate charge in relation to a received stimulus,
a pixel reset switch connected to a detector and to a discharge bus;
a pixel capacitor arranged to store the transducer output as a pixel charge on the capacitor (C p ),
a voltage amplifier connected to transfer the pixel voltage to a select switch,
a select switch line connected to the voltage amplifier via the select switch, wherein activating the select switch transfers the pixel voltage to the data tine and a data line charge is stored in a data line capacitor (C d ),
an amplifier select switch connected at one end to the data line, which may be used to multiplex a plurality of pixels or pixel rows;
a charge amplifier connected to a second end of the amplifier select switch, wherein, when the amplifier select switch is turned on, a full charge from the data line capacitor is sensed by the charge amplifier, the charge provided to the charge amplifier defined as the pixel charge multiplied by the data line capacitance (C d ) divided by the pixel capacitance (C p ); and
an external charge detector connected to the pixel, through use of a data line connector, the external charge detector comprised of a charge amplifier, a capacitance feedback, an amplifier reset switch, a sample and hold switch, and signal processing electronics.
12. The system according to claim 11 , wherein a capacitance of the pixel capacitor and a capacitance of the data line capacitor may be one of parasitic capacitance or extrinsic capacitance.
13. The system according to claim 11 wherein the transistors of the system include at least one of a-Si, p-Si, or organic transistors.
14. The system according to claim 11 , wherein the capacitance of the data line capacitor is used to generate noise-immune charge detection.
15. The system according to claim 11 , wherein
the pixel is one of a plurality of pixels arranged in a matrix of pixels, and
the amplifier select switch is one of a plurality of amplifier select switches, each amplifier select switch associated with one of a plurality of charge amplifiers.
16. A method of operating a charge gain hybrid imaging system having at least one pixel which transmits signal data to a charge amplifier, comprising:
activating an amplifier reset switch to reset the charge amplifier;
activating a pixel reset switch to reset the pixel;
deactivating the amplifier reset switch, wherein a gate-source capacitive charge is injected into a front end of the charge amplifier;
activating a sample switch a first time, wherein the gate-source capacitive charge is detected by the first sampling action, wherein an active state of an amplifier select switch encompasses the first active state of the sample switch;
deactivating the amplifier select switch, isolating the pixel from the charge amplifier;
activating a pixel select switch, wherein charge from a pixel capacitance of the pixel is transferred to a data line capacitance of a data line until a full data line charge is reached, and wherein the amplifier select switch remains inactive while the pixel select switch is active;
activating the amplifier select switch, wherein the charge of the data line capacitance is transferred to the charge amplifier as a charge gain defined by the relationship C d /C p ; and
activating the sample switch a second time, wherein an output of the charge amplifier due to the charge gain is detected.
17. The method according to claim 16 , wherein use of the first pulsing of the sample switch and pulsing of the second sample switch perform double correlated sampling.
18. The method according to claim 16 , wherein prior to the step of deactivating the amplifier reset switch, steps of
activating an amplifier reset switch to reset the charge amplifier, and
activating a pixel reset switch to reset the pixel, are performed.
19. The method according to claim 16 , wherein the amplifier select switches may be used to multiplex a plurality of pixels or pixel rows to a lesser number of charge amplifiers.